Signaling system



Aug. 9, 1938. H. s. BLACK ET AL 2,126,530

SIGNALING SYSTEM Filedan, 17, 193e HsLAc/f Nm/TOPS /c VAN rAssELPatented Aug. 9, 1938 UNITED STATES PATENT OFFICE SIGNALING SYSTEMHarold S. Black, Elmhurst, and Earl K. Van Tassel, Great Kills, N. Y.,assignors to Bell Telephone Laboratories,

Incorporated, New

7 Claims.

This invention relates to signaling systems and particularly to systemsfor giving fire alarms.

The objects of the invention are to obtain a more positive operation inthe performance of devices for detecting the presence of abnormaltemperatures; to lessen the likelihood of false operation; and ingeneral to improve and simplify re alarm systems.

It has been common practice to utilize fusible material, such as leadand lead alloys for detecting the presence of fire. In some cases thefusible material is in the form of wire and constitutes a part of anormally closed electric circuit, which is ruptured when the wire ismelted by excessive temperature and causes an alarm to sound. In othercases a spring contact is held out of engagement with a cooperatingcontact by an element of the fusible material. When the temperaturerises and melts the element, the spring contact is allowed to engage itscooperating contact, and the alarm circuit is closed. The reliability ofsystems of this kind depends entirely upon the fusible material, and thedifliculty sometimes encountered is that said material either is sosensitive that it melts in response to normal fluctuations in theambient temperature, thus giving a false alarm, or is too insensitive torespond to the higher temperatures, thereby delaying the alarm in theevent of fire.

A feature of the invention is to obviate these difficulties by a systemin which a resistor of some substance having a high negative temperaturecoeflicient of resistance, such as silver sulphide, is utilized tocontrol the flow of electric current through the fusible element. Byconnecting the resistor in series with the fusible element, the lcurrentflowing in the circuit can be made to rise rapidly from a negligibleamount to a very high value in responsive to any predetermined increasein the temperature of the environment.

Another feature of the invention is a system in which the resistor is solocated physically and electrically with respect to the fusible elementthat said resistor serves both to increase the heating current flowingin the element and also to transfer its own heat to the element. By suchan arrangement an added certainty is given to the attainment of themelting point of the fusible element when the predetermined abnormaltemperature is reached in the surrounding atmosphere.

These and other features and advantages of this invention will bediscussed more fully in detail in the following specification. Thedetailed specification should be considered in connection with theaccompanying drawing which:

Fig. 1 is an abbreviated illustration of a fire alarm system containinga temperature responsive device for controlling the alarm circuit, and

Figs, 2, 3, and 4 show modifications of the temperature responsivedevice.

It is well known that the substance silver sulphide has an extremelyhigh negative temperature coefficient of resistance. For example, it ispossible by raising the temperature of an element of this material tolower its resistance over a range extending from nearly a megohm tovalues less than 100 ohms. And this range of resistance values isobtainable by the use of temperatures from to 180 C. This sensitivenessof the material to changes in its temperature makes it especially wellsuited for fire alarm systems. Its temperature may be controlled by heatreceived from the surrounding medium, indicating the presence of fireand also by the resistance loss resulting from current flowing throughthe resistance material. These two causes contribute to produce a rapiddecrease in the resistance and consequently a rapid and large increasein the current flowing in the circuit containing the resistance element.

Referring now particularly to Fig. 1 of the drawing, the temperaturedetecting device here shown comprises as its essential elements acircuit closing spring I, a retaining link 2 of fusible material, aholding spring 3, and a resistor 4. The spring I is secured to the baseterminal and has sufficient resilience when released to engage thestationary circuit contact 6. however, the spring I is held away fromthe contact 5 by means of the link 2, which interconnects the spring Iand the extension arm 'I of the coiled holding spring 3, When properlyadjusted, the tension of the spring 3 is just sunlcient to hold thecontact spring I away from its cooperating contact 6. The link 2 may bemade of any suitable fusible material having sufficient tensile strengthto hold the spring contact I out of engagement with the contact 6. Itmay be in the form of a wire, a flat strip, or in any other desiredshape. The fusible temperature of the link 2 may be chosen at anydesired value. The resistor 4 is connected in circuit with the fusibleelement 2 and in circuit with the source of alternating current 8. Theresistor 4 may be placed in physical proximity to the element 2, or itmay be mounted in any other desired location. The unit 4 may be made ofany material having a high negative temperature coefficient of resist-Normally,

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ance. As above mentioned, however, we have found that silver sulphidecan be used to good advantage.

The operation of the system disclosed in Fig. 1 will now be explained.With the temperature responsive device set in its normal condition asseen in this figure, a circuit is traceable from the upper pole ofsource 8, over conductor 9, terminal block 5, through the spring contactI, fusible element 2, through the resistor 4, to the other pole of thesource 8. The resistance of the resistor 4 is so high at normal ambienttemperatures that only a negligible current can flow in the circuittraced. Assume, however, that a fire occurs in the region of theresistor 4. As the temperature increases above the usual variations inthe ambient temperature, the resistance of the element 4 decreasescorrespondingly, allowing more current to flow in the circuit. Thisadditional current produces heat in the element 4, causing itstemperature to increase still further, to produce in turn a furtherreduction in its resistance. This process continues, the current risingrapidly in the circuit including the resistor 4 and the fusible element2. When the current intensity flowing in the fusible element 2 reaches apredetermined value, as it soon will in response to the rapid decreasein the resistance of the element 4, the fusible element 2 melts andruptures the mechanical link that has been holding the spring I.Thereupon the spring I engages the contact 6 and closes an obviouscircuit for an alarm device I`.

In order to accentuate the heating effect in the fusible element 2, theresistor 4 may be placed physically adjacent the element 2. With such anarrangement the heat generated in the resistor 4 with the increase ofcurrent is transferred either by radiation or conduction to the fusibleelement 2. As the current in the circuit assumes larger and largervalues, a considerable amount of heat is generated in the resistor, andthis heat transferred to the element 2 contributes to a large extent inraising the temperature of the element to the fusing point.

The modification of the temperature responsive device shown in Fig. 2may be used instead of the construction illustrated in Fig. 1. In thismodified device the fusible element I I, which interconnects the contactspring I2 and the holding spring I3, is surrounded by and is in directphysical contact with the resistor I4. The resistor I4 is formed as acoating of silver sulphide around the fusible element II and isconnected by terminal conductors I5 and I6 to the source of current I'I.In this case an abnormal increase in the ambient temperature causes theresistor I4 to lower its resistance, permitting more and more current toflow from the source Il, in turn raising the temperature of the resistorI4 as the result of the increasing current. The heat thus generated bythe resistor I4 is applied directly to the fusible element II, and whenthe proper temperature is reached, this element ruptures. The resistorI4 may be so constructed that it does not have sufficient tensilestrength to hold the spring I2 after the fusible element II is ruptured.One way of accomplishing this result is to apply the silver sulphideresistor I4 in the form of a powder to the exterior of the fusibleelement I I.

In the modification shown in Fig. 3 the resistor I8 surrounds thefusible element I9 in somewhat the same manner as that illustrated inFig. 2. The resistor IB, however, is electrically insulated from themetallic fusible element I9 by means of a layer of electrical insulation2U interposed between the element I9 and the resistor I8. Thisinsulation makes it possible to include the resistor and the fusibleelement in series relation in the electrical circuit. The circuit may betraced from the upper pole of the source 2|, terminal 22, through theresistor I8, terminal 23, thence to the upper end of the fusible elementI9, through said element to the spring contact 24 and returning to theother pole of the source 2i. By this construction it is possible toobtain a more efficient heating relation between the resistor I8 and thefusible element I9 and at the same time to include the element I9 incircuit with the resistor. As explained in connection with Fig. 2, thetensile strength of the resistor I8 and the insulation 2D isinsuiiicient to interfere with the restoration of the spring 24 when thefusible link I 9 melts. For example, the insulator 20, as well as theresistor I8, may be made of material in amorphous form having lowtensile strength.

A further modification is illustrated in Fig. 4. Here the resistor 25 ismade in the form of a spiral conductor within which the fusible element26 is located. As shown, the fusible element 2G is raised to the fusingtemperature entirely by the heat transferred thereto from the resistor25. If desirable, however, the resistor 25 may also be connected inseries with fusible link 26 as shown in Figs. l and 3.

It is obvious that the location of these temperature detector deviceswithin the building to be protected may be made in accordance with awide variety of arrangements. constructed in any suitable form and itshould be understood that the structures described herein are merelyillustrative and do not limit the scope of the invention. Also thealternating current generators shown herein for supplying current to theresistance elements may be replaced by any suitable type of currentsource.

What is claimed is:

l. The combination in a signaling system of a fusible element, a circuitincluding said element, a source of potential connected to said circuit,a resistor having a high negative temperature coefficient of resistanceand responsive to other than normal ambient changes of temperature inthe surrounding medium for controlling the flow of current in saidcircuit, and a signal device actuated upon fusion of said fusibleelement.

2. In a signaling system, a current carrying fusible element, a circuitincluding said element, a resistor having a high negative temperaturecoefficient of resistance also included in said circuit and arranged totransfer its heat to said current carrying element, means for applying avolt age across said resistor, and signaling means actuated upon fusionof said current carrying element.

3. In a signaling system, a fusible element, a resistor having a highnegative temperature coefiicient of resistance and arranged to transferits heat to said element, a circuit including said element and resistor,means for applying a voltage across said resistor, and means renderedeffective by the fusing of said. fusible element.

4. In combination, a source of heating current and a circuit therefor, aresistor which responds to a change in temperature to cause an increasein the fiow of current of said circuit, an element in said circuit whichfuses in response to a predetermined current increase caused by saidresistor,

The elements may be and means responsive to the fusing of said element.

5. The combination in a signaling system of a circuit having a source ofcurrent connected thereto, a resistor in said circuit which lowers itsresistance and allows more current to ow to produce more heat therein inresponse to an increase in the ambient temperature, a fusible elementarranged in proximity to said resistor to receive transferred heat fromsaid resistor, and signal means actuated upon fusion of said fusibleelement.

6. The combination in a signaling system of a circuit having a source ofcurrenttherein, a resister of negative temperature coefiicient materialin said circuit which responds to other than normal changes in theambient temperature to cause an increased flow of current in saidcircuit and to produce heat, and a fusible control element arranged tobe heated by the increasing current flowing in said circuit and also toreceive transferred heat from said resistor.

7. In a signaling system, a fusible element and a circuit therefor, asource of current connected to said circuit, a resistor in said circuitwhich changes its resistance in response to changes in the ambienttemperature to allow an increased current to flow in said circuit andthrough said fusible element, a circuit making contact, a movablecontact normally held out of engagement with said first-mentionedcontact by said fusible element, and signal means rendered effectivewhen said fusible element fuses and allows said contacts to close.

HAROLD S. BLACK.

EARL K. VAN TASSEL.

